The present invention relates in general to telecommunication techniques. More particularly, the invention provides a method and system for mobile station handovers with various priorities in wireless networks. Merely by way of example, the invention is described as it applies to base-station initiated handovers, but it should be recognized that the invention has a broader range of applicability.
Techniques for wireless communications have progressed through the years. A wireless network usually includes base stations and mobile stations. For example, a mobile station (MS) refers to a station that is to be used while in motion or during halts at unspecified geographic locations. As an example, the mobile station is a mobile communication device. In another example, the mobile station is a cellular phone. In yet another example, a base station (BS) refers to a set of equipment that can provide connectivity, management, and control for one or more mobile stations. Often, a mobile station communicates with other devices through an air-interface provided by a base station. For example, the air-interface refers to an interface between the base station and the mobile station. Usually, the air-interface can be changes through a process called mobile station handover (HO). During handover, the mobile station, for example, can migrate from an air-interface provided by one base station to another air-interface provided by another base station. The handover can be initiated by either the mobile station or the base station for various reasons such as mobile-station movement, change in connection quality, and/or change in network configuration.
FIG. 1 shows a simplified conventional wireless network. The network 100 includes base stations 110, 112, and 114, and a mobile station 120. The base stations 110, 112, and 114 each are connected to a wired network 130. For example, the wired network 130 uses internet protocol (IP). The mobile station 120 communicates through an air-interface with the base station 110.
FIGS. 2 and 3 are simplified conventional diagrams for mobile-station handover in wireless network. In the network 100, the base station 110 sends a request message to the mobile station 120 to initiate a handover. The request includes a list of base stations to which the mobile station 120 can be handed over. If the mobile station 120 determines the requested handover to be suitable, the mobile station 120 selects one base station from the list and sends an acknowledgment message back to the base station 110. For example, in the acknowledge message, the mobile station 120 also informs the base station 110 that the base station 112 has been selected. Subsequently, the mobile station 120 is handed over to the base station 112.
FIGS. 4 and 5 are other simplified conventional diagrams for mobile-station handover in wireless network. In the network 100, the base station 110 sends a request message to the mobile station 120 to initiate a handover. The request includes a list of base stations to which the mobile station 120 can be handed over. As shown in FIGS. 4 and 5, if the mobile station 120 determines the requested handover is not suitable, the mobile station 120 sends a rejection message to the base station 110. In response, the base station 110 can send a response message that is used as another request and includes another list of base stations to which the mobile station 120 can be handed over. Additionally, the mobile station 110 can again reject the handover request in the response message, and in turn the base station 110 can continue the negotiation with the mobile station 120 by sending another response message as shown in FIG. 5.
FIGS. 6 and 7 show simplified conventional partial formats for request message and response message for handover respectively. As shown in FIGS. 6 and 7, the request message is called MOB_BSHO-REQ, and the response message is called MOB_BSHO-RSP. For example, the MOB_BSHO-REQ message is sent from the base station 110 to the mobile station 120 for initiating a handover. As another example, the MOB_BSHO-RSP message is sent from the base station 110 to the mobile station 120 in response to a rejection from the mobile station 120. The handover rejection by the mobile station and/or the handover negotiation between the mobile station and the base station may degrade network performance.
Hence it is highly desirable to improve techniques for mobile station handovers.